DESCRIPTION: Hispanic Americans will be the largest ethnic racial minority group by the year 2000. The comparatively higher prevalence of obesity among Hispanic Americans coupled with diets that are relatively higher in fat and lower in fiber may place Hispanic Americans at increased risk of cancer. Therefore, the investigators propose to develop and evaluate a cancer risk factor prevention program targeting pre-adolescents in schools serving predominantly low income Hispanic families that will include both a behavioral and an environmental component. Students in the study will receive interventions during both their fourth and fifth grade years. The prevention program will include a classroom-based intervention focusing on preventing obesity by a) increasing the perceived incentive value of adopting helpful eating and physical activity behaviors and b) providing instruction in weight regulation skills. Environmental intervention components will include a parent intervention coupled with the school intervention and a school food service intervention. The investigators will evaluate the efficiency of their comprehensive intervention in a cohort of 1100 underestimate from 14 elementary schools in the Alum Rock Union Elementary School District, in East San Jose, California. Students will be approximately 50 percent female, 70 percent Hispanic, 10 percent Asian, 7 percent white, 6 percent Filipino, 5 percent Black, 1 percent American Indian/Alaskan Native and 1 percent Pacific Islander. Seven schools will be randomly assigned to the comprehensive intervention, and the remaining seven schools will receive an attention placebo control intervention to minimize the potential for compensatory rivalry or resentful demoralization. Assessments of children's height, weight, tricep skinfold thickness, waste and hip circumferences, food preferences, cardiorespiratory fitness and self-reported behavior, attitudes and knowledge and Tanner Stage of development will occur at baseline (4th grade), post test (5th grade), and at 10-month follow-up (6th grade). Parent interviews will occur annually. A careful assessment of effects on parents and school personnel will be completed. However, the crucial question is whether the overall intervention has an impact on pre-adolescent obesity. The primary objective is to reduce the prevalence of obesity at the end of the two year intervention. Secondary objectives include reducing intake of dietary fat; increasing consumption of low fat foods, fruits, vegetables and dietary fiber; and increasing levels of moderate to vigorous physical activity. Finally, the investigators want to conduct risk assessment and targeting studies including response to treatment analyses.